I can't believe my son is going to elementary school next year, He is very excited, but I’m still worrying about him.
I can't believe my son is going to elementary school next year,
では、来年私の息子がもう小学校に行くなんて信じられない！と言う感じです。
I can't believe〜は、信じられない！
is going to 〜、未来での〜するを表します。
He is very excitedは、〜とっても楽しみにしてる。と言う意味です。
I’m still worrying about himは私は、とっても心配〜と言う意味です。
I can't believe he's starting elementary school next year
It's hard to believe he is starting elementary school next year
Children grow up so quick and things or stages in their life happen before you know or realise it to describe this you say 'I can't believe' or 'it's hard to believe'
子どもの成長は早く、気が付いたら人生の階段をまた一つ上っていたということがあります。
これについて伝えるなら、
'I can't believe'（信じられない）や、
'it's hard to believe'（信じられない）
と言えます。
It's hard to believe he is already starting elementary school next year!
To think that he's going to go to elmentary school next year is just crazy!
1. "It's hard to believe" means that it is difficult to fathom the reality of something.
2. "To think that" is a phrasing that puts the focus on the process of considering something. Stating that it is "just crazy" shows that it is hard to acknowldge the reality of something.
1. "It's hard to believe" は「～が現実だとは信じがたい」という意味です。
2. "To think that" は、物事を考えるプロセスに焦点を当てた言い方です。"just crazy" は「～を現実と受け入れるのは難しい」という意味です。
I can't believe he will be starting elementary school next year. My gosh, how time flies!
It's unbelievable that he will be starting elementary school next year. Time has gone by so quickly!
Since next year is in the future, you can use the future verb tense 'will be' before 'starting'. 'My Gosh' is an expression that expresses surprise at whatever a person is surprised at. In this case, it's the surprise that the child will already be starting elementary school next year. He/she was born not so long ago.
So, you may say:
I can't believe he will be starting elementary school next year. My gosh, how time flies!
or
It's unbelievable that he will be starting elementary school next year. Time has gone by so quickly!
「来年」は未来なので、'starting' の前に未来形の 'will be' を使っています。
'My Gosh' は驚きを表す表現です。この場合、子どもが来年小学生になることへの驚きです。「あっという間に大きくなった」ということです。
次のように言えます。
I can't believe he will be starting elementary school next year. My gosh, how time flies!
（来年小学生だなんて信じられない。時間がたつのは早い）
It's unbelievable that he will be starting elementary school next year. Time has gone by so quickly!
（来年小学生だなんて信じられない。本当にあっという間だった）
I simply can't believe he's starting infant school next year!
When talking about my son, and he will start elementary school next year - and you wish to explain this - and want to say it in a way that expresses that you can't believe he's starting elementary school already (It feels like time went by so fast), then you may try the abovementioned statement.
Elementary school: School attended by young children before they begin primary school.
"I can't believe he's starting elementary school next year"
To express sincere shock at the passing of time.
Watching your child grow is a very delicate experience.
Knowing that your child is now moving up a level in the world is an exciting realization.
It also comes with feelings of excitement and anxiety.
"I can't believe he's starting elementary school next year"（来年小学校だなんて信じられない）
時間の経過について強い衝撃を表します。
子どもの成長を見るのは複雑な気持ちですね。
子どもが社会の階段を一つ上がることというのは親にとって素晴らしいことですが、ただ同時にそれに対する不安もありますね。
My son will start elementary school next year! where has time gone?!
It's crazy to believe my son will be starting school soon!
"My son will start elementary school next year! where has time gone?!" "where will time go" is an expression used frequently when describing how quick time has gone past.
"It's crazy to believe my son will be starting school soon!" another phrase used frequently "I can't believe" can be used for a variety of contexts, "I can't believe my son starts school soon!" or "I can't believe I saved up enough money to buy a car!"
"My son will start elementary school next year! where has time gone?!"（息子が来年小学校に入学します。本当にあっという間です）
= "where will time go" は時間がたつのがあっという間だったことを表すときによく使われる表現です。
"It's crazy to believe my son will be starting school soon!"（息子がもうすぐ小学生だなんて信じられない）
= "I can't believe" も一般的なフレーズです。これはいろいろな文脈で使われます。
"I can't believe my son starts school soon!"（息子がもうすぐ小学生だなんて信じられない）
"I can't believe I saved up enough money to buy a car!"（自分が車を買えるだけのお金をためたなんて信じられない）
I can't believe he's starting elementary school next year!
My son is starting elementary school next year!
こんにちは。
I can't believe he's starting elementary school next year!
来年から小学校に行くなんて信じられません！
My son is starting elementary school next year!
息子は来年から小学校に行きます！
「小学校」は英語で elementary school / primary school と言います。
アメリカ英語では elementary school が一般的です。
対してイギリス等では primary school が使われることが多いです。
ぜひ参考にしてください。
日本 
イギリス 
アメリカ合衆国 
南アフリカ 
